SCANNING ELECTROCHEMICAL MICROSCOPY (SECM) OF FACILITATED ION TRANSFER AT THE LIQUID LIQUID INTERFACE/

A new mode of the scanning electrochemical microscope (SECM) operation is presented. A micropipette-based electrode is used as an amperometr ic microprobe (tip). The tip current is produced by facilitated transf er of ions from the aqueous solution inside the pipette into the organ ic solvent, e.g., the transfer of K+ into 1,2-dichloroethane (DCE) ass isted by dibenzo-18-crown-6 (DB18C6). A positive feedback current is o bserved when the tip approaches the water\DCE interface due to the tra nsfer of potassium into the aqueous layer and regeneration of DB18C6 s pecies. Good agreement with the SECM theory can be demonstrated. Negat ive feedback is observed when the tip approaches a glass insulator. Th e dependence of the SECM response on the shape of the liquid meniscus formed at the micropipette tip is discussed. The technique developed c an be used for studies of ion transfer processes at the liquid\liquid and liquid\membrane interfaces and for high resolution electrochemical imaging. (C) 1997 Elsevier Science S.A.